It has been reported that the size and shape of the pores depend on the structure of the base metal, the type of electrolyte, and the conditions of the anodizing process. The paper presents thin Al2O3 oxide layer formed under hard anodizing conditions on a plate made of EN AW-5251 aluminum alloy. The oxidation of the ceramic layer was carried out for 40–80 minutes in a three-component SAS electrolyte (aqueous solution of acids: sulphuric 33 ml/l, adipic 67 g/l, and oxalic 30 g/l) at a temperature of 293–313 K, and the current density was 200–400 A/m2. Presented images were taken by a scanning microscope. A computer analysis of the binary images of layers showed different shapes of pores. The structure of ceramic Al2O3 layers is one of the main factors determining mechanical properties. The resistance to wear of specimen-oxide coating layer depends on porosity, morphology, and roughness of the ceramic layer surface. A 3D oxide coating model, based on the computer analysis of images from a scanning electron microscope (Philips XL 30 ESEM/EDAX), was proposed.
We present an approach to the analysis of mechanisms of the tribological contact of a thin Al 2 O 3 oxide layer formed under hard anodizing conditions on a plate made of the aluminium alloy EN AW-5251. The oxidation of the 50-lm ceramic layer was carried out for 60 min in a three-component electrolyte (SAS), a three-component electrolyte consisting of adipic, sulphuric and oxalic acid, at a temperature of 298.15 K and a current density of 3 A/dm 2. A three-dimensional oxide coating model, based on the computer analysis of images from a scanning electron microscope, is proposed. Tribological tests of stresses, strains and dislocations formed in the oxide layer and in the sample material (a block) were conducted. Modified polytetrafluoroethylene (TG15, TGK20/5, TMP12) and polyetheretherketone with carbon fibre and graphite were used as samples for tests in the tribological couple rider-plate of a linear reciprocating friction tester. A tribological couple modelled in the Solid Edge CAD programme was subjected to numerical analyses using the finite element method in the Autodesk Simulation Multiphysics programme under conditions consistent with actual conditions for contact pressures of 0.25, 0.50, and 1.0 MPa.
This article describes the research findings achieved by the application of Al2O3 nano-layers coated on aluminum alloys by an electrolytic method. With tribological applications, mainly thin and hard anti-wear coatings were used. Oxide Al2O3 nano-layers created by electrolytic method on aluminum alloys have very good tribological properties when pairing them with plastics and low friction composites. Self-lubricating coatings are a mixture of binding and lubricating agents, which after a putting on sliding surfaces create the coating being characterized by a low friction coefficient that enables a mutual movement of the rubbing areas without the need to apply an extra lubrication media. On the other hand, binding materials – polymers – guarantee the presence of the cohesive force which hold components of the layers together, as well as adhesive forces binding the layer with the base. Practically all polymers can be applied as a matrix for production of polymer composites, but because of excellent friction properties and chemical inertness polytetrafluoroethylene is the most attractive. The structure of the investigated nano-layers was described by the computer image analysis that enables its modeling. Analyzed nano-layers were tribological tested in pair with composites on the basis of polytetrafluoroethylene. In the course of examinations tribological properties were measured that described the quality of sliding pairs, i.e. friction coefficient and abrasive wear. The registered parameters were compared to these measured in other tribological pairs. The differences were analyzed and justified. For predicting stresses and strains generated during the experiment a finite element method was used. The achieved results are similar to the measured real values. Applied computer analysis with finite element method as the calculation method of the cube-plate sliding matching with reciprocating motion and simulation of real forces condition that affect the system, allowed to achieve the following maximal stresses: TG15 (3.02726 MPa), TGK20/5 (3.02732 MPa), TMP12 (4.25076 MPa), and strains: TG15 (0.0045573), TGK20/5 (0.0047507), TMP12 (0.0065434). The stress distributions indicate that the highest values appear in the contact cube-plate area and at the lower cube edges especially in the places being in accordance with the movement direction irrespective of the kind of material used. Material modification results in the change of achieved stresses and strain values according Hooke’s law.
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